1. Technical Field
The present invention relates to a foam spraying apparatus according to the introductory part of the claim 1.
2. Description of the Related Art
A foam spraying device of such type is known e.g. from the International Patent Application WO-A-93/13829. There a foam spraying device is described with a container containing a foamable liquid, a valve, a delivery opening for the foam generated as well as a sieve between the delivery opening and the valve for obtaining the desired mixture of liquid and air. Furthermore between the valve and the sieve a perforated disk is provided in which the perforations in the form of holes or slots are arranged along the periphery in order to better mix liquid and air. By using a pump a pressure within the container is built up. A conventional spraying nozzle shall be moved against the force of a pressure spring towards the container body so that the air is entered and mixed with the liquid by means of the sieve and the perforated disk in such a manner that a foam is formed and is given off at the delivery opening.
This known foam spraying device comprises a multitude of individual parts made from various materials such as synthetic materials and metals. Manufacture of a foam spraying device of this type thus is rather expensive. It is a further disadvantage of the known foam spraying device that for generating sufficient pressure within the container the pump must be operated several times before foam can be delivered.
Furthermore from the European Patent Application EP-A-0 392 238 a foam spraying device is known with a shifting piston or media pump for the liquid and an air compressor pump each provided with an inlet valve and an outlet valve. The air compressor pump is arranged on the same axis with, and adjoining, the media pump, both pumps being operated at the same time using a cap-shaped handle. In this arrangement the back piston end of the shifting piston pump is provided with a long piston shaft in which a shaft with a disk-shaped valve closing element is arranged. A set-back spring is provided between the bottom wall and the valve closing element. For generating foam a mixing chamber with an adjacent foaming body is provided.
This foam spraying device also comprises a great number of individual elements which present particularly complex shapes in order to ensure correct co-operation. Due to the line-up of the air compressor pump and the media pump this device is of considerable length which impedes operation.
On the other hand from the French Patent Application FR-A-2 317 969 a spray device is known which comprises two pumps, one for the air and one for the liquid, arranged between the spray head and the liquid container. The liquid pump consists of two tubes shiftable inside each other of which tubes the lower one can be closed against the liquid container by a valve body with a hollow plunger. The spraying cap also forms the cylinder of the air pump which can be moved up and down inside a shorter cylinder portion of a larger diameter. The spraying cap furthermore is provided in its upper zone with a spraying nozzle with a mixing chamber which via valve-like structures is connected to the air pump and the liquid pump. Using a very complex design lay-out with small ducts the connection is ensured between the cylinder elements and the air pump and the liquid pump. No mixing chamber with a foaming body being provided and thus no foam can be generated using the proposed spraying device.
The spaying device so described also comprises a great many individual parts made from various materials. The intake tube e.g. is made from extruded polythene and the spraying cone is injection moulded from polythene. The valve body and the plunger can be made from low density polythene.
It is the objective of the present invention to improve a foam spraying apparatus of the type described above in such a manner that it comprises a substantially reduced number of individual parts and permits foam generation in a simple manner.
These objectives are met using an apparatus presenting the characteristics according to the patent claim 1.
The inventive foam spraying apparatus for a liquid container with an air suction device, a mixing chamber for the air and liquid blend and a spaying head with a foam delivery opening comprises between the spraying head and the liquid container a first piston and cylinder unit for the air and a second piston and cylinder unit for the liquid each provided with an inlet valve and an outlet valve which co-operate being mutually coupled. Thus the inventive foam spraying apparatus presents the substantial advantage that in one manual movement air is compressed as well as liquid is expulsed whereas during expansion of the spraying head air and liquid are sucked in again. In this fast and simple manner a large quantity of foam can be generated without application of the usual propellant gases. The inventive foam spraying apparatus furthermore is characterised in that the cylinder of the first unit and the piston of the second unit are interconnected to an intermediate part and that the piston and the cylinder of the second unit are interconnected to a base part in such a manner that the intermediate part and the base part engage one another movable relative to each other.
In an advantageous embodiment of the present invention the cylinder of a first unit and the piston of the second unit form a unit body as intermediate part and the piston of the first unit and the cylinder of the second unit form a unit body as base part. In a further advantageous embodiment the piston of the second unit is laid out eccentrically with respect to the first unit. In this arrangement a space saving engagement of the two piston and cylinder units is obtained A further variant is laid out in such a manner that the piston of the second unit is arranged concentrically with the cylinder of the first unit, i.e. inside the latter unit. This presents the advantage that the insert containing the mixing chamber is shorter and thus an optimum layout of the foam spraying apparatus can be achieved It proves advantageous to provide the pistons of both units each with a sealing ring in order to ensure optimal intake of air and liquid.
Advantageously the mixing chamber is formed by an insert between the spraying head and the intermediate element. In this arrangement the mixing chamber can present a tapered inlet opening for the air and a tapered inlet opening for the liquid. For correct foam generation it has proven advantageous if after the air inlet opening and after the liquid inlet opening, as seen in the flow direction, a fine mesh sieve is provided. It has proven particularly advantageous if a foaming chamber with a second fine mesh sieve is provided. In practical use it has proven useful if the spraying head, the insert, the intermediate element, and the base part are made from an injection moulded hard synthetic material.
Manufacture of the foam spraying apparatus advantageously is effected using injection moulding of a two-component synthetic material. Particularly proven is if simultaneously the elements serving as valves and as sealing rings made from a rubber plastic synthetic material in the injection moulding process are surrounded by the corresponding elements coordinated to them.
Manufacture of the inventive foam spraying apparatus thus is much simpler and more cost-efficient as only a small number of individual parts is required.